Search Results (49)

Traditional coal quality assessment methods rely exclusively on the laboratory testing of physical samples, which impedes detailed stratigraphic evaluation and limits the integration of intelligent precision mining technologies. To resolve this challenge, this study investigates geophysical logging as an innovative method for coal quality prediction. By integrating scanning electron microscopy (SEM), X-ray analysis, and optical microscopy with interdisciplinary methodologies spanning mathematics, mineralogy, and applied geophysics, this research analyzes the coal quality and mineral composition of the Shanxi Formation coal seams in northern Jiangsu, China. A predictive model linking geophysical logging responses to coal quality parameters was established to delineate relationships between subsurface geophysical data and material properties. The results demonstrate that the Shanxi Formation coals are gas coal (a medium-metamorphic bituminous subclass) characterized by low sulfur content, low ash yield, low fixed carbon, high volatile matter, and high calorific value. Mineralogical analysis identifies calcite, pyrite, and clay minerals as the dominant constituents. Pyrite occurs in diverse microscopic forms, including euhedral and semi-euhedral fine grains, fissure-filling aggregates, irregular blocky structures, framboidal clusters, and disseminated particles. Systematic relationships were observed between logging parameters and coal quality: moisture, ash content, and volatile matter exhibit an initial decrease, followed by an increase with rising apparent resistivity (LLD) and bulk density (DEN). Conversely, fixed carbon and calorific value display an inverse trend, peaking at intermediate LLD/DEN values before declining. Total sulfur increases with density up to a threshold before decreasing, while showing a concave upward relationship with resistivity. Negative correlations exist between moisture, fixed carbon, calorific value lateral resistivity (LLS), natural gamma (GR), short-spaced gamma-gamma (SSGG), and acoustic transit time (AC). In contrast, ash yield, volatile matter, and total sulfur correlate positively with these logging parameters. These trends are governed by coalification processes, lithotype composition, reservoir physical properties, and the types and mass fractions of minerals. Validation through independent two-sample t-tests confirms the feasibility of the neural network model for predicting coal quality parameters from geophysical logging data. The predictive model provides technical and theoretical support for advancing intelligent coal mining practices and optimizing efficiency in coal chemical industries, enabling real-time subsurface characterization to facilitate precision resource extraction. Full article

Organic matter pores constitute a significant storage space in shale gas reservoirs, contributing to approximately 50% of the total porosity. This study employed a comprehensive approach, utilizing scanning electron microscopy, low-pressure N₂ adsorption, thermal analysis, image statistics, and fractal theory, to quantitatively characterize the structure and complexity of organic matter pores in the Wufeng–lower Longmaxi Formations (WLLFs). The WLLFs exhibit a high organic matter content, averaging 3.20%. Organic matter pores are typically well-developed, predominantly observed within organic matter clusters, organic matter–clay mineral complexes, and the internal organic matter of pyrite framboid. The morphology of these pores is generally elliptical and spindle-shaped, with the primary pore diameter displaying a bimodal distribution at 10~40 nm and 100~160 nm, potentially influenced by the observational limit of scanning electron microscopy. Shales from greater burial depths within the same gas well contain more organic matter pores; however, the development of organic matter pores in deep gas wells is roughly equivalent to that in medium and shallow gas wells. Fractal dimension values can be utilized to characterize the complexity of organic matter pores, with organic matter macropores (D_>50) being more complex than organic matter mesopores (D_2–50), which in turn are more complex than organic matter micropores (D_<2). The development of macropores and mesopores is a key factor in the heterogeneity of organic matter pores. The complexity of organic matter pores in the same well increases gradually with the burial depth of the shale, and the complexity of organic matter pores in deep gas wells is roughly equivalent to that in medium and shallow gas wells. The structure and fractal characteristics of organic matter pores in shale are primarily controlled by components, diagenesis, tectonism, etc. The lower Longmaxi shale exhibit a high biogenic quartz content and robust hydrocarbon generation from organic matter. This composition effectively shields organic matter pores from multi-directional extrusion, leading to the formation of macropores and mesopores without specific orientation. High-quality shale sections (one and two sublayers) have relatively high fractal dimension D_2–50 and D_>50 values of organic matter pores and gas content. Consequently, the quality parameters of shale and fractal dimension characteristics can be comprehensively evaluated to identify high-quality shale sections. Full article

A combination of microstructural, fluid inclusion, and in situ sulfur isotopic analyses of pyrite, along with major and trace element studies of the mineralization-hosting sandstone, reveals the complexity of its genesis from the Jurassic Toutunhe Formation in the Liuhuanggou sandstone-hosted uranium deposit, Southern Junggar Basin. Based on field geological investigations and the geochemical characteristics, it is concluded that the source of the ore-bearing sandstones originates from felsic igneous rocks in the Northern Tianshan and Central Tianshan regions. Through optical microscopy and scanning electron microscopy (SEM), three generations of pyrite were identified: framboidal pyrite, concentric overgrown pyrite, and sub-idiomorphic to idiomorphic cement pyrite. The sulfur isotopes of the pyrite were analyzed using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The results indicate that each type of pyrite has distinct sulfur isotope compositions (the framboidal pyrite: −16.85‰ to +2.16‰, the concentric overgrown pyrite: −7.86‰ to +10.32‰, the sub-idiomorphic to idiomorphic cement pyrite: +9.16‰ to +16.77‰). The framboidal pyrite and the sub-idiomorphic to idiomorphic cement pyrite were formed through bacterial sulfate reduction (BSR), while the concentric overgrown pyrite was formed through thermochemical sulfate reduction (TSR) triggered by the upward migration of hydrocarbons. The discovery of hydrocarbon inclusions provides evidence for the involvement of deep-seated reducing fluids in uranium mineralization. Uranium mineralization occurred in two distinct stages: (1) The early stage involved the interaction of uranium-bearing fluids with reductants in the mineralization-hosting strata under the influence of groundwater dynamics, leading to initial uranium enrichment. (2) The later stage involved the upward migration of deep-seated hydrocarbons along faults, which enhanced the reducing capacity of the sandstone and resulted in further uranium enrichment and mineralization. Full article

Authigenic minerals in shale are products of the co-evolution of organic and inorganic components, affecting the heterogeneity of shale reservoirs. However, due to their fine granularity and complex rock composition, studies on these minerals in shale are still insufficient. This research focuses on the lacustrine shales from the upper sub-member of the fourth member in the Eocene Shahejie Formation, Dongying Sag, East China. Utilizing core samples, thin sections, scanning electron microscope, X-ray diffraction, elemental geochemistry, and organic geochemistry, we systematically characterized the features and origins of authigenic minerals. The results identified several typical authigenic minerals, including authigenic quartz, framboidal and euhedral pyrite, ferroan dolomite, kaolinite, chlorite, and albite. Authigenic quartz is predominantly diagenetic silica formed through smectite illitization, acidic dissolution of K-feldspar, and alkaline dissolution of detrital quartz. Pyrite is a product of microbial sulfate reduction, with framboidal pyrite forming during an early diagenetic stage under conditions with sufficient solute supply and euhedral pyrite forming during a later stage under conditions with insufficient solute supply. Ferroan dolomite originates from the precipitation of Fe and Mg during smectite illitization, with slight contributions from the acidic dissolution of chlorite and calcite. Kaolinite stems from the acidic dissolution of K-feldspar, while chlorite results from the transformation of kaolinite. Albite primarily arises from the alkaline alteration of anorthite and K-feldspar. Most non-clay authigenic minerals likely enhance reservoir quality by slightly reducing the effects of compaction, whereas authigenic clay minerals typically exert detrimental effects on reservoir properties. This study constrains the genesis of authigenic minerals to assess their influence on reservoir quality in lacustrine shale. Full article

This study focuses on the Hailijing sandstone-hosted uranium deposit in the Songliao Basin. Through a combination of petrographic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and geochemical analysis, the epigenetic alteration of the deposit was systematically investigated, and the alteration zonation was delineated. On this basis, the metallogenic mechanisms were further explored. The results indicate that six major types of alteration can be identified in the ore-bearing strata of the Hailijing uranium deposit: hematitization, limonitization, carbonatization, pyritization, clay mineralization (including kaolinite, illite, and illite-smectite mixed-layer), and baritization. The mineral assemblages at different stages of alteration vary: during the sedimentary diagenetic stage, the assemblage consists of “hematite + clay minerals + II-type pyrite (framboidal pyrite) + III-type pyrite (euhedral granular pyrite)”; during the uranium mineralization stage, it transitions to “ankerite + barite + I-type pyrite (colloidal pyrite) + minor kaolinite”; and in the post-ore stage, alteration is characterized by calcite cementation in red sandstones. Based on petrological, mineralogical, and geochemical characteristics, as well as the spatial distribution of the host gray sandstones, it is inferred that during uranium mineralization stage, the ore-bearing strata underwent reduction by uranium-rich reducing fluids sourced from the Lower Cretaceous Jiufotang Formation. The primary red sandstones of the Lower Yaojia Formation, formed under arid to semi-arid conditions, experienced varying degrees of reduction, resulting in a color transition from light red, brownish red, and yellowish brown to grayish-yellow and gray. Accordingly, four alteration zones are distinguished in the Hailijing uranium deposit: the primary red zone, weakly reduced pink zone, moderately reduced grayish-yellow zone, and strongly reduced gray zone. Furthermore, as the uranium-rich reducing fluids migrated from a high-temperature, high-pressure deep system to the low-temperature, low-pressure ore-bearing sandstone strata near the surface, uranium was unloaded, precipitated, and enriched, ultimately forming multi-layered and tabular-shaped uranium orebodies within the gray sandstone. This study elucidates the epigenetic alteration processes and metallogenic mechanisms of the Hailijing uranium deposit, providing a critical theoretical basis for further uranium exploration in the southern Songliao Basin. Full article

The Ordovician/Silurian boundary (Wufeng/Longmaxi formations) in the Shizhu region, eastern Sichuan Basin, China hosts organic-rich black shales which are frequently interbedded with bentonite and hydrothermal minerals (e.g., pyrite). This study investigated the mineralogical, total organic carbon (TOC), total sulfur (TS), and major and trace element compositions of organic-rich samples. Non-visible volcanic input is identified to influence organic matter accumulation, as shown by the correlations between TOC and proxies, including Zr and Hf contents and the Cr/Al₂O₃, V/Al₂O₃, Ni/Al₂O₃, and SiO₂/Al₂O₃ ratios. Redox indicators (V/Cr, v/v + Ni, degree of pyritization (DOP), U/Th, and Mo contents) display positive correlations with TOC values, suggesting that an oxygen-depleted environment is necessary for organic matter (OM) preservation. The TOC values exhibit better regression coefficients (R²) against redox indicators, including DOP (0.43), U/Th (0.70), and Mo contents (0.62), than V/Cr (0.16) and v/v + Ni (0.21). This may because some V, Cr, and Ni is hosted in non-volcanic ashes within shales but not inherited from contemporaneous water columns. The greater scatter in TOC-DOP and TOC-Mo relative to TOC-U/Th relations may result from hydrothermal venting in shales, evidenced by the coexistence of framboid and euhedral pyrite and the previous finding of hydrothermally altered dolomites in the studied sections. There is no systematic relation between TOC and Ni/Co ratios, and this means that portions of Ni are contributed by non-visible volcanic ashes and Ni and Co are redistributed during the precipitation of hydrothermal pyrites due to their strong chalcophile affinities. Such a feature may further suggest that most pyrites are precipitated during hydrothermal venting. The DOP displays broad correlations with non-visible volcanic indicators, supporting that hydrothermal venting may be triggered by volcanic activities. The outcomes of this study highlight that caution is necessary when evaluating the sedimentary facies features of volcanism-affected organic-rich black shales with the used metallic proxies. Full article

A set of organic-rich black shales has developed in the lower Gaojiabian Formation (Lower Silurian) in the Lower Yangtze region, South China. However, limited research on its paleoenvironment and the mechanisms of organic matter enrichment has hindered further analysis of shale gas exploration prospects in this area. Utilizing samples from the Akidograptus ascensus to Cystograptus vesiculosus graptolite biozones in the Gaojiabian Formation obtained from well SY-1, we analyzed geochemical elements and pyrite framboids to reconstruct paleoenvironmental characteristics and paleoproductivity, revealing factors influencing organic matter enrichment. The results indicate that the total organic carbon (TOC) content and paleoproductivity levels of the shale are both high, with a significant enrichment of redox-sensitive elements. Additionally, the pyrite framboids are well developed, characterized by small particle sizes and a narrow range of variation. This study reveals that during this period, the region generally developed a perennial oxygen minimum zone (P-OMZ) environment, accompanied by transient euxinic conditions during the Akidograptus ascensus and the early stages of Parakidograptus acuminatus and Cystograptus vesiculosus. This situation represents the extension of the Rhuddanian Oceanic Anoxic Event (R-OAE) into the Lower Yangtze region, where the water body exhibited moderate restrictions. Compared to paleoproductivity indicators, there is a stronger positive correlation between TOC and the redox-sensitive elements vanadium (V), molybdenum (Mo), and uranium (U) in the samples. This finding indicates that the P-OMZ and euxinic environments of the Lower Yangtze Sea were the key factors influencing organic matter enrichment in the Akidograptus ascensus to Cystograptus vesiculosus biozones. Consequently, the overall pattern of organic matter enrichment was predominantly determined by preservation conditions. Full article

The Nevşehir coals are located in the Central Anatolian Crystalline Complex (CACC), Türkiye, and no reports exist on trace element, nitrogen, and carbon isotope composition data of the Nevşehir coals. The present study aims to geochemically characterise the Nevşehir coals to determine their trace elemental enrichment patterns and possible sources. Nevşehir coals are found within Late Miocene Kızılöz Formation (Arafa Member) rocks. These coals are part of the huminite maceral group; the dominant maceral group is ulminites. The minerals in coals are inorganic, such as oxidised framboidal pyrite, iron oxide minerals, quartz, clay, and carbonate minerals. Coals have great potential regarding trace elements. Benefits might arise from mining and using some of the critical elements derived from coal. Compared with the world coal average, the coal samples in this study are enriched in As (149.25 μg/g), V (245 μg/g), Cr (159 μg/g), Ga (18 μg/g), Ni (216 μg/g), Th (17 μg/g), Zn (143 μg/g), and U (54 μg/g). The arsenic content in this study is associated with inorganic components such as oxidised framboidal pyrite. Vanadium in coal is mainly associated with aluminosilicates and organic matter. Chromium originates from the clay minerals within coals. Uranium in coal is mainly associated with organic matter. Nickel and zinc in coal are predominantly associated with sulphides. The δ¹⁵N contents of the samples are comparable to those of several references, including plants, terrestrial creatures, and organic nitrogen. The δ¹³C–δ¹⁵N isotopic range and average values for four coal samples ranged from −25.66‰ to −25.91‰ (−25.80‰) and 3.6‰ to 4.3‰ (3.9‰), respectively, demonstrating that C3 type modern terrestrial vegetation was common in the palaeomires of the studied coal seams. Full article

The Mazarrón 2 shipwreck was found in 1994 on the beach of Playa de la Isla (Mazarrón, Murcia, Spain). This finding is extremely important because the boat and its lead cargo were still in a reasonable conservation state and, therefore, provided new data on naval construction, commercial goods, navigation routes, and the relationships between the Phoenicians and the local population in the 7th–6th century BC. Currently, the shipwreck remains underwater, protected by a metallic coffer. In the last 2 years, a Preliminary Studies Project has been carried out, supported by national and regional public institutions. This research aims to know the shipwreck’s conservation state and to determine the extraction and conservation methods at the Museo Nacional de Arqueología Subacuática ARQVA (Cartagena, Spain), where the conservation and restoration treatment will be conducted. The sampling strategy and analytical study included not only wood and other materials from the shipwreck and its cargo but also the seawater and the seabed materials in the vicinity of the shipwreck. This paper presents the results of the geochemical study of the archeological site. The applied methodology included physico-chemical tests, X-ray diffraction, optical microscopy, FTIR spectroscopy, field-emission scanning electron microscopy coupled with X-ray microanalysis, and X-ray microscopy. The results indicated that, despite the wreck being buried at a shallow depth (less than 50 cm) in a marine environment with a water column of 2–2.5 m, influenced by complex coastal dynamics that favor an oxic environment, early diagenetic processes like the formation of pyrite framboids are particularly intense in the pores and internal channels of the wreck’s wood, where a different dysoxic–anoxic environment prevails. These processes have been the main mechanisms to have affected the wreck and are related to the biogeochemistry of sediments. The sediments have been confirmed to be closely related to the geological context of the Mazarrón region. The conducted study found no significant evidence of pollution due to the lead cargo. Full article

Iran hosts more than 350 Precambrian to Cenozoic sediment-hosted Zn-Pb±Ba and barite-sulfide deposits, including shale-hosted massive sulfide (SHMS, also called SEDEX) and Irish-type and Mississippi Valley-type (MVT) mineralization, and barite is a common mineral in these deposits. In the SHMS deposits, barite is typically found as fine-grained disseminations in thin laminae. In these deposits, the sulfide laminae often occur as diagenetic replacements and as bands containing authigenic and diagenetic barite and pyrite framboids. In the Irish-type Zn-Pb-Ba and stratabound barite-sulfide deposits, barite exhibits various textures, including fine-grained disseminated barite, banded zebra textures, veins, and massive barite lenses. In some of the giant Irish-type deposits, as well as in the stratabound barite-sulfide mineralization, the main stratabound sulfide ore is developed within a barite envelope and is characterized by the replacement of barite and pyrite by chalcopyrite, galena, and sphalerite. In the MVT deposits, the formation of barite is often related to dolomitization, and sulfide mineralization involves the replacement of the dolomitized carbonate rocks, as well as associated barite. Fluid inclusion studies on the Irish-type deposits indicate that the temperatures and salinities of the sulfide-forming fluids are higher compared to those of the barite-forming fluids. Fluid inclusion analyses of coarse-grained barites from Irish and MVT deposits reveal their hydrothermal origin. The δ³⁴S values of sulfide minerals (pyrite, sphalerite, and galena) in Irish-type deposits exhibit a broad range of low values (mostly −28 to +5‰), primarily revealing a process of bacterial sulfate reduction (BSR). However, the textures (replacement, colloform, and banded) and more positive sulfur isotope values (+1 to +36‰) in the SHMS Zn-Pb deposits suggest that bacterial sulfate reduction (BSR) plays a less significant role. We suggest that thermochemical sulfate reduction (TSR) connected to the direct replacement of barite plays a more relevant role in providing sulfur for the sulfide mineralization in the SHMS, barite-sulfide, and MVT deposits. Based on the textual evidence, sulfur isotopic data, and fluid inclusion studies, barite has been identified as a key controller for the subsequent Zn-Pb mineralization by providing a suitable host and significant sulfur contribution in the sediment-hosted Zn-Pb and stratabound barite-sulfide deposits. This implies that diagenetic barite might be a precursor to all types of sediment-hosted Zn-Pb mineralization. Full article

In order to investigate the effect of primary productivity, organic matter dilution, and preservation on the accumulation of organic matter, geochemical data, and proxies of primary productivity, clastic influx, and redox conditions were obtained for organic-rich shales in the Cambrian Niutitang Formation. The primary productivity (total organic carbon [TOC], Mo, P, Ba, and Babio) and redox (Ni/Co, V/Cr, U/Al, and Th/U) proxies suggest the organic-rich shales were deposited in anoxic-euxinic conditions during periods of high primary productivity. Pyrite in the Niutitang Formation comprises spherical framboids, which also indicate that anoxic bottom waters were present during organic matter deposition. High primary productivity enhanced the organic C flux into the thermocline layer and bottom waters, which lead to the development of anoxic bottom waters owing to O₂ consumption by microorganisms and organic matter degradation. The anoxic bottom waters were beneficial for the preservation of organic matter. In addition, Ti/Al ratios correlate well with TOC contents throughout the Niutitang Formation, indicating that clastic input increased the burial rate and prevented organic matter degradation during deposition. Therefore, the accumulation of organic matter in the Niutitang Formation was controlled mainly by primary productivity rather than bottom-water redox conditions. Full article

Selenium and Te are two important critical metals, which are often produced as by-products in Au-Cu deposits related to magmatic–hydrothermal systems, such as porphyry and skarn deposits. The Jilongshan Au-Cu deposit is a typical skarn deposit located in the middle and lower parts of the Yangtze River metallogenic belt. Previous studies show that it has valuable Se and Te resources, but their occurrence, particularly the relationship between the texture and composition of pyrite, and the enrichment mechanism of Se, Te, and Au remain unclear. Here, the textures and the major and trace elements of the Jilongshan pyrites were studied by using an optical microscope, EMPA, and LA-ICP-MS to reveal the occurrence of Se, Te, and Au in pyrite, as well as their genetic links with the pyrite mineralogical signature. The results show that there are three types of ores in the Jilongshan deposit, including granite porphyry-hosted, skarn-hosted, and carbonate-hosted ores. All of these ores contain major amounts of pyrite, which can be divided into four different generations. The first generation of pyrite (Py1) belongs to sedimentary genesis with a typical framboid texture and its Co/ Ni ratios are less than 1, whereas Py2, Py3, and Py4 belong to hydrothermal genesis and their Co/ Ni ratios are between 1.0 and 30.2. Selenium concentrations in Py2 and Py3 are relatively high (median, 138 ppm and 344 ppm, respectively), which are mainly present as isomorphism and a small amount as selenite in pyrite. Compared with granite porphyry-hosted and skarn-hosted ores, pyrite from carbonate-hosted ores has the highest Se concentrations. The latest generation of pyrite (Py4) contains the highest concentrations of Te (average, 140 ppm) and Au (average, 12 ppm) among the hydrothermal pyrites. Therefore, the precipitation of Se mainly occurs in pyrite during the early high-temperature stage, whereas higher concentrations of Te and Au are mainly enriched in pyrite during the late stage with low temperatures. Full article

The Rio Muni Basin is a hotspot for deep-water oil exploration in West Africa. The discovery of thirteen oil and gas fields, including Ceiba, Akom 1, and Oveng, proves the basin’s excellent exploration prospects, but only limited research has thus far been carried out there. The recent new drilling indicates that there are organic matter-rich fine-grained sedimentary rocks in the Albian and Cenomanian–Turonian stages of the Cretaceous strata. However, the depositional models of organic-rich, fine-grained sedimentary rocks are not clear. The main objectives of this study are as follows: (1) to identify the lithofacies characteristics of fine-grained sedimentary rocks in the Albian–Turonian stages of the Rio Muni Basin; and (2) to establish a depositional model for organic-rich fine-grained sediments. In this study, the mineralogical characteristics of Albian–Turonian fine-grained were determined by means of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and thin section analysis. In addition, the integration of mineralogical features with the total organic carbon (TOC) content allows for the recognition of three distinct lithofacies: (1) siliceous-clayey rock, (2) terrigenous clastic mixed fine-grained rock, and (3) lime-mixed fine-grained rock. Based on the evolutionary history of the passive continental margin basins in West Africa and the lithofacies characteristics, the deposition mode of organic-rich fine-grained sedimentary rocks in the Albian–Turonian stages was reconstructed by combining geochemical features with the characteristics of framboidal pyrite. The depositional models for the Albian stage are “continental margin–restricted sea–marine algae–source rocks” with the development of organic-rich fine-grained sedimentary rocks. The depositional models for the Cenomanian–Turonian stage are “continental margin–semiopen sea–mixed-source rocks”. The Albian and Cenomanian–Turonian organic-rich fine-grained sedimentary rocks represent two different deposition modes with restricted sea and semiopen sea conditions. The sedimentary characteristics in the study area during the two periods were both inherited and notably different. Full article

Fine-grained organic matter (OM) particles are commonly widely dispersed in shale deposits. However, carrying out investigations of pores hosted by OM particles and the nature of grain interactions in OM particles and associated detrital grains using optical microscopy is difficult at best. Scanning electron microscopy (SEM) is much better suited for characterizing the microstructure of dispersed OM particles and has found wide application in the study of unconventional oil and gas systems. Scanning electron microscopy was used to define the types of OM contained in marine shale deposits of the Wufeng and Longmaxi Formations spanning the Ordovician–Silurian transition in South China. Of particular interest was the development of OM-hosted pores and the identification of the factors that controlled their formation. The dominant OM type contained in the studied deposits is pyrobitumen, with subordinate graptolitic OM and sparse OM of unknown origin. Pyrobitumen is present in four forms, including pore fillings among authigenic quartz grains, within framboidal pyrite, and between authigenic clay grains and massive material. Diagenetic alteration has given rise to OM pores of differing morphology, size, and time of formation. Common small, equisized circular or oval OM pores are most developed and appear to have formed in association with the generation of hydrocarbons. Shale deposits containing abundant pyrobitumen filling interparticle pores among authigenic quartz crystals display robust reservoir and fracturing capacity. A sedimentary environment appears to have been the main factor affecting the type of OM and the nature of its association with detrital and authigenic minerals. Results of this study demonstrate that a sedimentary environment is a primary requisite for the formation of highly prospective/high-yielding hydrocarbon shale reservoir deposits. Full article

The Mangbang Formation in the Hanbazhai area is part of the uranium ore field in the Longchuanjiang Basin, China. Uraniferous sandstones from this formation are examined in this study. The type and mode of occurrence of uranium are investigated in detail using an experiment for the sequential extraction of uranium, as well as an electron probe, scanning electron microscopy, and energy spectrum analyses. The sequential extraction experiment indicates that the proportion of uranium minerals is significantly greater than that of the adsorbed uranium in the samples, with the latter being largely present in framboidal pyrites and clay minerals. The results show that these uranium minerals are mainly composed of coffinite and uranium phosphosilicates, which closely coexist with framboidal pyrites, carbon debris, feldspar minerals, and clay minerals. The discovery of coffinite and uranium phosphosilicates is discussed in context with their symbiotic relationship and geochemical environment. Uraniferous sandstones are considered to have undergone at least two stages of mineralization: the sedimentary–diagenetic stage and the later uranium enrichment by fluid. The geochemical environment of the sedimentary–diagenetic stage is generally a sulfide-reducing environment, and the later fluids are rich in U, Si, P, and Y. Full article